U.S. patent application number 14/448260 was filed with the patent office on 2015-03-05 for coagulation processing method, coagulation processing unit, and water processing apparatus.
This patent application is currently assigned to Hitachi, Ltd.. The applicant listed for this patent is Hitachi, Ltd.. Invention is credited to Satoshi ISHII, Kenji OKISHIRO, Hiroshi SASAKI.
Application Number | 20150060367 14/448260 |
Document ID | / |
Family ID | 52581664 |
Filed Date | 2015-03-05 |
United States Patent
Application |
20150060367 |
Kind Code |
A1 |
ISHII; Satoshi ; et
al. |
March 5, 2015 |
COAGULATION PROCESSING METHOD, COAGULATION PROCESSING UNIT, AND
WATER PROCESSING APPARATUS
Abstract
The present invention provides a coagulation processing method
capable of adding a sufficiently-dissolved coagulant aqueous
solution to being processed water and materializing high-efficiency
coagulation processing, a coagulation processing unit, and a water
processing apparatus. A coagulation processing unit includes a
coagulant aqueous solution storage tank 1 to have a stirrer 5 and
store a coagulant aqueous solution, a particle size distribution
measurement device 50 to measure the particle size distribution of
the coagulant aqueous solution in the coagulant aqueous solution
storage tank 1, a coagulation tank 11 to mix being processed water
with an added coagulant aqueous solution and form a coagulation, a
coagulation removing section 9 to remove the coagulation from the
being processed water containing the coagulation, and a control
section 6 to control the stirrer 5 so that a median size in the
particle size distribution of the coagulant aqueous solution may be
not more than 1.0 .mu.m on the basis of a measured particle size
distribution.
Inventors: |
ISHII; Satoshi; (Tokyo,
JP) ; OKISHIRO; Kenji; (Tokyo, JP) ; SASAKI;
Hiroshi; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hitachi, Ltd. |
Tokyo |
|
JP |
|
|
Assignee: |
Hitachi, Ltd.
|
Family ID: |
52581664 |
Appl. No.: |
14/448260 |
Filed: |
July 31, 2014 |
Current U.S.
Class: |
210/709 ;
210/143; 210/702; 210/723; 210/724; 210/728 |
Current CPC
Class: |
C02F 2209/11 20130101;
C02F 2209/05 20130101; C02F 2209/20 20130101; C02F 1/441 20130101;
C02F 1/54 20130101; C02F 2209/06 20130101; C02F 2103/08 20130101;
C02F 2209/02 20130101; C02F 1/685 20130101; C02F 1/5209 20130101;
C02F 1/5245 20130101; C02F 2209/36 20130101 |
Class at
Publication: |
210/709 ;
210/702; 210/723; 210/728; 210/143; 210/724 |
International
Class: |
C02F 1/52 20060101
C02F001/52; C02F 1/44 20060101 C02F001/44; C02F 1/54 20060101
C02F001/54 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 28, 2013 |
JP |
2013-176183 |
Claims
1. A coagulation processing method for removing impurities from
being processed water containing the impurities, comprising: a step
for adding one or plural kinds of coagulant aqueous solutions to
said being processed water containing the impurities; and a step
for forming a coagulation wherein a median size in the particle
size distribution of said one or plural coagulant aqueous solutions
is not more than 1.0 .mu.m.
2. A coagulation processing method according to claim 1, wherein a
coagulation is formed by adding an inorganic coagulant aqueous
solution to said being processed water, and a polymer coagulant
aqueous solution is added to said being processed water after said
coagulation is formed.
3. A coagulation processing method according to claim 2, wherein
said median size in said particle size distribution of said polymer
coagulant aqueous solution is in the range of not less than 1.4 nm
to not more than 1.0 .mu.m.
4. A coagulation processing method according to claim 1, wherein pH
of said coagulant aqueous solution is adjusted to not more than
1.0.
5. A coagulation processing method according to claim 1, wherein an
addition quantity of said coagulant aqueous solution is decided on
the basis of water quality data of said being processed water and
said median size in said particle size distribution of said
coagulant aqueous solution.
6. A coagulation processing method according to claim 2, wherein
said inorganic coagulant aqueous solution is any one of aluminum
sulphate, ferric chloride, ferric sulfate, aluminum chloride,
aluminum sulfate, and polyaluminum chloride.
7. A coagulation processing method according to claim 2, wherein
said polymer coagulant aqueous solution is any one of a
polyacrylamide system coagulant, a polysulfonic acid system
coagulant, a polyacrylic acid system coagulant, a polyacrylic acid
ester system coagulant, polyamine system coagulant, and a
polymethacrylic acid coagulant.
8. A coagulation processing method according to claim 5, wherein
said water quality data of said being processed water includes at
least any one of total organic carbon (TOC), turbidity, water
temperature, pH, electroconductivity, protein, saccharide (neutral
sugar, acidic sugar), and adenosine triphosphate (ATP)
activity.
9. A coagulation processing unit comprising: a coagulant aqueous
solution storage tank having a stirrer, which stores a coagulant
aqueous solution; a particle size distribution measurement device
which measures a particle size distribution of said coagulant
aqueous solution in said coagulant aqueous solution storage tank; a
coagulation tank which mixes being processed water with an added
coagulant aqueous solution, and form a coagulation; a coagulation
removing section which removes said coagulation from said being
processed water containing said coagulation; and a control section
which controls said stirrer so that a median size in said particle
size distribution of said coagulant aqueous solution may be not
more than 1.0 .mu.m on the basis of a measured particle size
distribution.
10. A coagulation processing unit according to claim 9, wherein
said coagulant aqueous solution is an aqueous solution of an
anionic polymer coagulant.
11. A coagulation processing unit according to claim 9, further
comprising: a water quality inspection section which measures
quality of said being the processed water; wherein said control
section decides a quantity of said coagulant aqueous solution added
to said being processed water on the basis of said measured quality
of said being processed water and a particle size distribution
obtained from said particle size distribution measurement
device.
12. A coagulation processing unit according to claim 11, wherein
said water quality inspection section includes a first water
quality inspection section which measures quality of said being
processed water and a second water quality inspection section which
measures quality of said being processed water from which the
coagulation is removed, and said control section decides a quantity
of said coagulant aqueous solution added to said being processed
water on the basis of the measurement results obtained from said
first water quality inspection section, said second water quality
inspection section, and said particle size distribution measurement
device.
13. A coagulation processing unit according to claim 9, wherein
said coagulant aqueous solution storage tank includes a first
storage tank to store an inorganic coagulant aqueous solution and a
second storage tank to store a polymer coagulant aqueous solution,
and said coagulation tank includes a first coagulation tank to mix
said inorganic coagulant aqueous solution introduced from said
first storage tank with said being processed water and a second
coagulation tank installed at the rear stage of said first
coagulation tank to mix said being processed water containing said
coagulation introduced from said first coagulation tank with said
polymer coagulant aqueous solution introduced from said second
storage tank.
14. A water processing apparatus comprising: a coagulant aqueous
solution storage tank having a stirrer, which stores a coagulant
aqueous solution; a particle size distribution measurement device
which measures the particle size distribution of said coagulant
aqueous solution in said coagulant aqueous solution storage tank; a
coagulation tank which mixes being processed water with an added
coagulant aqueous solution and form a coagulation; a coagulation
removing section which removes said coagulation from said being
processed water containing said coagulation; a separation section
which applies membrane separation processing to said being
processed water introduced from said coagulation removing section;
and a control section which controls said stirrer so that a median
size in the particle size distribution of said coagulant aqueous
solution may be not more than 1.0 .mu.m on the basis of a measured
particle size distribution.
15. A water processing apparatus according to claim 14, wherein
said being processed water is seawater and said coagulant aqueous
solution is an aqueous solution of an anionic polymer coagulant,
and said separation section has a reverse osmosis membrane (RO
membrane) and separates concentrated water of a high saline
concentration from fresh water by said reverse osmosis
membrane.
16. A water processing apparatus according to claim 14, wherein
said control section controls a stirring speed of said stirrer so
that a median size in the particle size distribution of said
coagulant aqueous solution may be in the range of not more than 1.0
.mu.m.
17. A water processing apparatus according to claim 15, wherein a
pH adjuster is added so that the pH of said coagulant aqueous
solution in said coagulant aqueous solution storage tank may be not
more than 1.0.
18. A coagulation processing method according to claim 2, wherein
an addition quantity of said coagulant aqueous solution is decided
on the basis of water quality data of said being processed water
and said median size in said particle size distribution of said
coagulant aqueous solution.
19. A coagulation processing method according to claim 3, wherein
an addition quantity of said coagulant aqueous solution is decided
on the basis of water quality data of said being processed water
and said median size in said particle size distribution of said
coagulant aqueous solution.
20. A coagulation processing method according to claim 3, wherein
said inorganic coagulant aqueous solution is any one of aluminum
sulphate, ferric chloride, ferric sulfate, aluminum chloride,
aluminum sulfate, and polyaluminum chloride.
21. A coagulation processing method according to claim 3, wherein
said polymer coagulant aqueous solution is any one of a
polyacrylamide system coagulant, a polysulfonic acid system
coagulant, a polyacrylic acid system coagulant, a polyacrylic acid
ester system coagulant, polyamine system coagulant, and a
polymethacrylic acid coagulant.
22. A coagulation processing unit according to claim 11, wherein
said coagulant aqueous solution storage tank includes a first
storage tank to store an inorganic coagulant aqueous solution and a
second storage tank to store a polymer coagulant aqueous solution,
and said coagulation tank includes a first coagulation tank to mix
said inorganic coagulant aqueous solution introduced from said
first storage tank with said being processed water and a second
coagulation tank installed at the rear stage of said first
coagulation tank to mix said being processed water containing said
coagulation introduced from said first coagulation tank with said
polymer coagulant aqueous solution introduced from said second
storage tank.
Description
CLAIM OF PRIORITY
[0001] The present application claims priority from Japanese Patent
application serial No. 2013-176183, filed on Aug. 28, 2013, the
contents of which are hereby incorporated by reference into this
application.
FIELD OF THE INVENTION
[0002] The present invention relates to a coagulation processing
method for adding a coagulant to being processed water and forming
a coagulation, a coagulation processing unit, and a water
processing apparatus having the coagulation processing unit.
BACKGROUND OF THE INVENTION
[0003] As water-purification technologies to produce drinking water
and utility water from natural water such as river water, chemical
methods such as a coagulating sedimentation method and physical
methods such as a sand filtration method have been considered.
[0004] Meanwhile in recent years, water shortage is a challenge in
all the countries of the world including Middle East and Asia. In
response to that, a seawater desalination technology to produce
drinking water and utility water by desalinating seawater attracts
attention and begins to be practically used. As a method for
desalinating seawater, an evaporation method of obtaining fresh
water by heating the seawater, thus evaporating water, and cooling
the vapor has been used. The evaporation method however has a poor
energy efficiency and is costly and hence a more efficient method
has been desired. At present, a reverse osmosis method of obtaining
fresh water by using a reverse osmosis membrane (RO membrane) and
desalinating seawater through membrane filtration comes to be a
main stream. In order to prevent an RO membrane from being
polluted, it is necessary to apply appropriate preprocessing for
removing suspended matters, organic matters, etc. before seawater
is applied to the RO membrane. As a method of the preprocessing,
membrane filtration by using an ultrafiltration (UF) membrane or a
microfiltration (MF) membrane, the use of an absorbent such as
activated carbon, or the use of a coagulant is studied in the same
way as water purification processing.
[0005] As typical coagulants for sewage treatment or water
purification processing, inorganic coagulants using polyvalent
metallic ions (cations) comprising polyaluminum chloride (PAC) or
iron chloride, polymer coagulants using water-soluble polymers
having polyvalent ions, and the like are named. Such a coagulant
removes electrically-charged impurities contained in water by
coagulation and sedimentation. Meanwhile, in the case of obtaining
an insufficient effect even when either an inorganic coagulant or
an organic coagulant is used, it is sometimes possible to enhance
the coagulation effect by using an inorganic coagulant and an
organic coagulant in combination.
[0006] JP-A No. 2002-136809 describes an apparatus to produce an
aqueous solution when a polymer coagulant is used and discloses an
apparatus having a mechanism of measuring the concentration of the
dissolved polymer coagulant aqueous solution.
[0007] JP-A No. 2008-264723 discloses a method of coagulating
impurities by adding an organic coagulant and an inorganic
coagulant simultaneously or in this sequence and adjusting pH when
the impurities in water such as seawater or river water are
removed.
[0008] JP-A No. H10-225682 discloses a method of removing boron by
adjusting pH with a pH adjuster and then adding a coagulant for
removing boron when seawater is purified.
[0009] In any of JP-A No. 2002-136809, JP-A No. 2008-264723, and
JP-A No. H10-225682 however, the function of measuring a particle
size distribution in a coagulant aqueous solution is not provided
and it is impossible to judge whether or not a coagulant dissolves
sufficiently in an aqueous solution. Consequently, if a polymer
coagulant is used as the coagulant and coagulation processing is
applied by adding an insufficiently-dissolved coagulant aqueous
solution, the coagulation efficiency lowers and the coagulant is
consumed more than necessary.
[0010] The present invention provides a coagulation processing
method capable of materializing highly-efficient coagulation
processing by adding a sufficiently-dissolved coagulant aqueous
solution to processed water, a coagulation processing unit, and a
water processing apparatus.
SUMMARY OF THE INVENTION
[0011] In order to solve the problems, a coagulation processing
method of the present invention comprises a step for adding one or
more kinds of coagulant aqueous solutions to be processed water
containing impurities, thus forming a coagulation, and a step for
removing the formed coagulation, thereby the impurities in being
processed water are removed, and is characterized in that controls
a median size in the particle size distribution of the coagulant
aqueous solution to not more than 1.0 .mu.m.
[0012] Further, a coagulation processing unit of the present
invention is characterized in that comprises a coagulant aqueous
solution storage tank having a stirrer to store a coagulant aqueous
solution, a particle size distribution measurement device to
measure the particle size distribution of the coagulant aqueous
solution in the coagulant aqueous solution storage tank, a
coagulation tank to mix being processed water with an added
coagulant aqueous solution and form a coagulation, a coagulation
removing section to remove the coagulation from the being processed
water containing the coagulation, and a control section to control
the stirrer so that a median size in the particle size distribution
of the coagulant aqueous solution may be not more than 1.0 .mu.m on
the basis of a measured particle size distribution.
[0013] According to the present invention, it makes it possible to
provide a coagulation processing method capable of adding a
sufficiently-dissolved coagulant aqueous solution to be processed
water and materializing highly-efficient coagulation processing, a
coagulation processing unit, and a water processing apparatus.
[0014] When a polymer coagulant is used as a coagulant for example,
since it is possible to disperse the coagulant uniformly in being
processed water and improve coagulation processing efficiency, it
is possible to reduce a medical agent in a coagulation process and
reduce the operation cost of a water processing apparatus.
[0015] Other problems, configurations, and effects than described
above will be obvious by explaining the following embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a general configuration diagram of a water
processing apparatus having a coagulation processing unit according
to the present invention;
[0017] FIG. 2 is another general configuration diagram of a water
processing apparatus having a coagulation processing unit according
to the present invention;
[0018] FIG. 3 is still another general configuration diagram of a
water processing apparatus having a coagulation processing unit
according to the present invention;
[0019] FIG. 4 is yet another general configuration diagram of a
water processing apparatus having a coagulation processing unit
according to the present invention;
[0020] FIG. 5 is a table explaining the relationship between a
particle size distribution and the trap of impurities;
[0021] FIG. 6 is a table explaining the relationship between a
particle size distribution and a processed water quality at each of
the embodiments;
[0022] FIG. 7 is a table explaining the relationship between a
particle size distribution and a processed water quality at each of
the comparative examples; and
[0023] FIG. 8 is a graph showing the relationship between an acidic
sugar rejection ratio and the ascension rate of clogging
(filtration pressure).
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] A coagulation processing method, a coagulation processing
unit, and a water processing apparatus according to an embodiment
of the present invention are explained hereunder. The present
invention is characterized by controlling a median size (d50) in
the particle size distribution of a polymer coagulant aqueous
solution used for coagulation processing to not more than 1.0
.mu.m. Here, a median size means the size of a particle located in
the center when particles are aligned in the order of size and is
generally described as d50. By injecting a polymer coagulant
aqueous solution in the state of being dissolved in sufficiently
small particle sizes, it is possible to disperse a coagulant into
being processed water swiftly and uniformly, and to apply
coagulation processing of a high efficiency. It is still better to
control the pH of a coagulant aqueous solution to an acid state
(not more than pH 2, preferably not more than pH 1) when being
processed water is salty water of a high concentration such as
seawater. This is caused by the dissociation state of a coagulant
and is explained on the basis of an anionic polymer. A carboxyl
radical included in an ordinary anionic polymer coagulant exists in
water in such an equilibrium state as described below. In an acid
region, the equilibrium shifts toward the left and the dissociation
of the carboxyl radical is inhibited. That is, when a polymer
coagulant aqueous solution is acidized, a carboxyl radical of an
anionic polymer in an aqueous solution is in an undissociated
state. Then when the polymer coagulant aqueous solution is added to
salty water of a high concentration as it is, divalent ions (Mg,
Ca, etc.) in being processed water can be inhibited from combining
and it does not happen that a coagulation is formed
instantaneously. As a result, it is desirably estimated that a
polymer coagulant coagulating before targeted impurities are
trapped can be reduced to the greatest possible extent and a
medical agent and a cost can be reduced.
--COOH.revreaction.--COO.sup.-+H.sup.+ (Formula 1)
[0025] FIG. 1 is a general configuration diagram of a water
processing apparatus having a coagulation processing unit according
to the present invention. The present invention: is explained
hereunder on the basis of the case of using a seawater desalination
apparatus as a water processing apparatus; but is not limited to
the case; and is applicable likewise to a processing apparatus for
industrial effluent and a processing apparatus for sewage such as
domestic sewage. In FIG. 1 further, the flow of water is
represented by sold arrows and signal lines (control lines) are
represented by dotted lines.
[0026] As shown in FIG. 1, a water processing apparatus according
to the present invention includes a coagulant aqueous solution
storage tank 1, a first water quality inspection section 7 to
measure the quality of seawater to be processed water, a
coagulation tank 11 to add a polymer coagulant aqueous solution to
the being processed water and to apply coagulation processing, a
filtration section 9 to separate and remove a coagulation from the
being processed water after coagulation reaction, a second water
quality inspection section 8 to measure the quality of the being
processed water after the coagulation is removed, a reverse osmosis
membrane unit (hereunder referred to as an RO membrane unit) 10 to
remove a saline matter from the being processed water from which
the coagulation is removed, and a control section 60 to control
them. The RO membrane unit 10 removes ions such as chloride ions
and sodium ions from the being processed water from which the
coagulation is removed. Further, the filtration section 9 is
configured by appropriately placing any one or a combination of a
sedimentation tank (sedimentation section), an ultrafiltration
section, a microfiltration section, a sand filtration tank (sand
filtration section), and a multimedia filtration section, for
example. Then the filtration section 9 separates and removes the
coagulation produced by making impurities in the being processed
water trapped by a coagulant in the coagulation tank 11 from the
being processed water. Here, in the general configuration of the
water processing apparatus shown in FIG. 1, the configuration
excluding the RO membrane unit 10 is called a coagulation
processing unit.
[0027] The coagulant aqueous solution storage tank 1 has a stirrer
5 to stir a polymer coagulant aqueous solution, a branched channel
20 used for measuring a particle size distribution, and a particle
size distribution measurement device 50 installed at the branched
channel 20 and used for measuring the particle size distribution of
the polymer coagulant aqueous solution. The particle size
distribution measurement device 50 includes a flow cell 2 to flow
the polymer coagulant aqueous solution, a laser irradiation section
3 to irradiate the polymer coagulant aqueous solution flowing in
the flow cell 2 with a laser, and a detection section 4 disposed so
as to interpose the flow cell 2 and face the laser irradiation
section 3. The detection section 4 detects a scattered light
intensity by receiving scattered light generated by irradiating the
coagulant in the polymer coagulant aqueous solution with a laser
and converting the light into electricity. Then the detection
section 4 obtains the distribution of the particle sizes of the
coagulant in the polymer coagulant aqueous solution on the basis of
a scattered light intensity distribution, and outputs the
distribution to a coagulant addition rate control section 6. The
coagulant addition rate control section 6 thereby obtains a median
size (d50) in the particle size distribution of the polymer
coagulant aqueous solution in the coagulant aqueous solution
storage tank 1.
[0028] Although the particle size distribution measurement device
50 is explained here on the basis of the case of measuring a
particle size distribution by a dynamic light scattering method at
a flow cell 2, a laser irradiation section 3, and a detection
section 4, in addition to the method, particle size distribution
measurement methods such as a laser diffraction method, a picture
imaging method, and a gravity sedimentation method are known for
example. The laser diffraction method is a method of obtaining
particle sizes from the intensity distributions of diffraction
light and scattered light obtained by irradiating particles with a
laser. Further, the picture imaging method is a method of obtaining
a picture of particles with an optical microscope, an electron
microscope, or the like and obtaining the sizes of the particles
from the picture image. The gravity sedimentation method is a
method of dispersing an analysis sample uniformly in a solvent and
obtaining a particle size distribution from the sedimentation
velocities of the particles. Furthermore, although a particle size
distribution measurement device 50 includes a flow cell 2, a laser
irradiation section 3, and a detection section 4 in the present
invention, the present invention is not limited to that. For
example, it is also possible to, configure a particle size
distribution measurement device 50 with a fiber for laser
irradiation and a fiber for light receiving disposed closely so as
to be perpendicular to it, and to install the particle size
distribution measurement device 50 in a coagulant aqueous solution
storage tank 1. On this occasion, it is unnecessary to install a
branched channel 20 in the coagulant aqueous solution storage tank
1.
[0029] In FIG. 1 further, a stirrer 12 is installed in the
coagulation tank 11 and the speed of stirring fins can be
controlled by controlling the rotation frequency of a motor. That
is, a stirring intensity is controllable. Here, a stirring
intensity is determined from the capacity of a coagulation tank,
the area of stirring fins, the rotation frequency of the stirring
fins (stirring speed), and others but the stirring intensity is
controlled by controlling the rotation frequency of the stirring
fins because the capacity and the area of the stirring fins are
constant.
[0030] The operation of a water processing apparatus shown in FIG.
1 is explained hereunder. Firstly, the quality of introduced being
processed water is measured at a first water quality inspection
section 7. The specific measurement items of the water quality are
a total organic carbon (TOC) concentration, water temperature, pH,
and turbidity for example. On this occasion, the particle size
distribution of a polymer coagulant aqueous solution stored in a
coagulant aqueous solution storage tank 1 is measured beforehand
with a particle size distribution measurement device 50.
Successively, after the being processed water is taken in a
coagulation tank 11, a coagulant addition rate control section 6
controls a pump 13 and adds an optimum amount of polymer coagulant
aqueous solution from the coagulant aqueous solution storage tank 1
to the coagulation tank 11 on the basis of the quality data of the
being processed water and the data of the particle size
distribution of the polymer coagulant aqueous solution measured at
the first water quality inspection section 7 (feedforward control).
After the polymer coagulant is sufficiently activated with a
stirrer 12 in the coagulation tank 11, a coagulation is removed at
a filtration section 9. Successively, the quality of the being
processed water from which the coagulation is removed is measured
at a second water quality inspection section 8. The coagulant
addition rate control section 6 decides a highly precise and
optimum addition quantity of a polymer coagulant aqueous solution
and adds the quantity decided to the being processed water by
feedback control on the basis of the water quality data measured at
the second water quality inspection section 8 and the particle size
distribution data of the polymer coagulant aqueous solution. The
coagulant addition rate control section 6 stores the relationship
of water quality data, the particle size distribution data of the
coagulant aqueous solution, and an optimum addition quantity of a
coagulant beforehand in a memory section not shown in the figure.
Here, it is more desirable to configure the coagulant aqueous
solution storage tank 1 so as to have a pH measurement mechanism
and monitor and control the pH of the polymer coagulant aqueous
solution, and install a mechanism allowing a pH adjuster to be
added.
[0031] As a polymer coagulant in a polymer coagulant aqueous
solution stored in a coagulant aqueous solution storage tank 1, any
one of a polyacrylamide system coagulant, a polysulfonic acid
system coagulant, a polyacrylic acid system coagulant, a
polyacrylic acid ester system coagulant, a polyamine system
coagulant, and a polymethacrylic acid coagulant can be used. In the
case of a polymer having a carboxyl radical of a small acid
dissociation constant in particular, the speed at which the polymer
is ionized when added to seawater is low and hence impurities can
be trapped more effectively.
[0032] A mechanism of trapping impurities in being processed water
by a polymer coagulant is explained hereunder. FIG. 5 is a table
explaining the relationship between a particle size distribution
and the trap of impurities.
[0033] In FIG. 5, when a median size (d50) in the particle size
distribution of a polymer coagulant aqueous solution is small, a
polymer coagulant dissolves sufficiently and uniformly and is added
to being processed water in a coagulation tank 11 in the state
where the polymer chains are separated from each other. In
contrast, when a median size (d50) is large, a polymer coagulant
dissolves insufficiently and is added to being processed water in a
coagulation tank 11 in the state where an association is formed by
entanglement between polymer coagulant molecules or the like. In
FIG. 5, in the case of a small median size (d50) in comparison with
the case of a large median size (d50), it is possible to trap more
impurities in processed water by one polymer chain, thereby make
the polymer chain act on more impurities in the being processed
water, and to process the coagulation more efficiently. To that
end, by processing coagulation while measuring the particle size
distribution of a polymer coagulant aqueous solution and confirming
that it is an appropriate particle size distribution, the
coagulation processing can be more efficient. As a result,
advantages including the reduction of a medical agent quantity
caused by the optimization of a coagulant addition rate, the
reduction in the risk of a harmful effect caused by excessive
addition of a medical agent, and the like can be obtained.
[0034] Although the above explanations have been made on the basis
of a polymer coagulant, the same consideration can be applied to an
inorganic solvent. That is, it is estimated that, if the median
size (d50) of a coagulant aqueous solution is large, an inorganic
coagulant does not ionize and is in the state of forming an
association and a coagulation before it is added to being processed
water and that leads to the lowering of the effect when the
inorganic coagulant is added to the being processed water. For that
reason, when two kinds of coagulants of an inorganic coagulant and
a polymer coagulant are used as the coagulants for example, it is
desirable to measure the particle size distributions of both the
inorganic coagulant and the polymer coagulant in an aqueous
solution. In the case of a polymer coagulant in particular, the
influence is conspicuous and hence the effect is large.
[0035] Explanations in the case of applying a polymer coagulant to
high-concentration salty water are made hereunder on the basis of
applying an anionic polymer coagulant. When a carboxyl radical is
added in a dissociated state as shown in Formula 1, instantaneously
the carboxyl radical combines with microflocs, Mg, Ca, etc. in
seawater that is salty water of a high concentration by
electrostatic interaction and forms a coagulation. In contrast,
when the pH of an aqueous solution of an anionic polymer coagulant
is lowered, the equilibrium in Formula 1 shifts toward the right
and a carboxyl radical is added to seawater in an undissociated
state. On that occasion, unlike the above case, a time lag is
caused from the addition of a coagulant to the formation of a
coagulation and the anionic polymer can physically trap more
microflocs in the meantime. As a result, the efficiency of a
coagulant can be improved by lowering the pH of an aqueous solution
containing an anionic polymer coagulant. Further, when a steady
state is reached, the equilibrium constant of Formula 1 is
determined by the pH of being processed water, thus the pH of the
being processed water also influences coagulation efficiency, and
hence it is possible to form a coagulation more effectively by
adding a pH adjuster when a polymer coagulant is added.
[0036] A configuration of measuring the quality of introduced being
processed water (seawater) at a first water quality inspection
section 7 and measuring the quality of the being processed water
after a coagulation is removed at a second water quality inspection
section 8 is shown in FIG. 1 and the measurement of water quality
is explained hereunder.
[0037] Information on water quality (water quality data) of being
processed water and water quality data of processing water are
obtained by sensing substances (total organic carbon (TOC) and
turbidity) contained in introduced being processed water. Feedback
and feedforward control is carried out by using the water quality
data measured at the first and second water quality inspection
sections 7 and 8. A coagulant addition rate control section 6
decides the addition quantities of various coagulants suitable for
the quality of the introduced being processed water (water quality
data measured at the first water quality inspection section 7). As
a result, it is possible to materialize a maximum coagulant
efficiency by the optimization of the addition quantities of the
coagulants, prevent excessive addition of the coagulants and
inhibit unnecessary sludge from being generated, and to optimize
the operation cost of a water processing plant.
[0038] The measured water quality data, besides the above data, are
water temperature, pH, electroconductivity, protein, saccharide
(neutral sugar, acidic sugar), adenosine triphosphate (ATP)
activity, and others and an index of an organic component or an
inorganic component contained in the processed water that is
estimated to influence the fouling (clogging) of an RO membrane
unit 10 may desirably be included in the water quality data to be
measured.
[0039] In FIG. 1, a first water quality inspection section 7 and a
second water quality inspection section 8 are installed at the
front stage of a coagulation tank 11 and at the rear stage of a
filtration section 9, respectively. The purpose is to optimize
coagulation processing with a high degree of accuracy. For
simplification however, it is also possible to install either of
the water quality inspection sections and carry out the evaluation
of water quality and the control of a coagulant addition rate.
[0040] A coagulant addition rate control section 6 not only decides
a quantity of a polymer coagulant aqueous solution added to being
processed water in a coagulation tank 11 but also controls the
stirring intensity of a stirrer 5 installed in a coagulant aqueous
solution storage tank 1 so that a median size (d50) in the particle
size distribution of the polymer coagulant aqueous solution stored
in the coagulant aqueous solution storage tank 1 may be not more
than 1.0 .mu.m. Here as stated earlier, a stirring intensity is
determined by the capacity of a tank, the area of stirring fins,
the rotation frequency of the stirring fins (stirring speed), and
others but the stirring intensity is controlled by controlling the
rotation frequency of the stirring fins because the capacity and
the area of the stirring fins are constant.
[0041] A water processing apparatus in the case of using two kinds
of coagulants is explained hereunder. FIG. 2 is another general
configuration diagram of a water processing apparatus having a
coagulation processing section according to the present invention.
Constituent components identical to FIG. 1 are represented by
identical reference numerals. The water processing apparatus is
configured by further installing a first coagulant aqueous solution
storage tank 31 to store an inorganic coagulant aqueous solution
and a coagulation tank 21 to add the inorganic coagulant aqueous
solution to being processed water and process coagulation in the
water processing apparatus explained in FIG. 1. The coagulation
tank 21 to add the inorganic coagulant aqueous solution and process
coagulation is referred to as a first coagulation tank and the
coagulation tank 11 to add a polymer coagulant aqueous solution and
process coagulation is referred to as a second coagulation tank
hereunder. As the inorganic coagulant, any one of aluminum
sulphate, ferric chloride, ferric sulfate, aluminum chloride,
aluminum sulfate, and polyaluminum chloride is used for
example.
[0042] In the configuration of the water processing apparatus shown
in FIG. 2, it is desirable to install particle size distribution
measurement devices 50 in both the first coagulant aqueous solution
storage tank 31 to store an inorganic coagulant aqueous solution
and the second coagulant aqueous solution storage tank 1 to store a
polymer coagulant aqueous solution but here the configuration of
installing a particle size distribution measurement device 50 only
in the second coagulant aqueous solution storage tank 1 is adopted.
The operations of the water processing apparatus shown in FIG. 2
are explained. An inorganic coagulant aqueous solution stored in
the first coagulant aqueous solution storage tank 31 is fed to the
first coagulation tank 21 through a pump 14. Further, a polymer
coagulant aqueous solution stored in the second coagulant aqueous
solution storage tank 1 is fed to the second coagulation tank 11
connected to the rear stage of the first coagulation tank 21
through a pump 13. A stirrer 22 and a stirrer 12 are installed in
the first coagulation tank 21 and the second coagulation tank 11
respectively and the speeds of stirring fins can be controlled by
controlling the rotation frequencies of motors. Here, the inorganic
coagulant aqueous solution and the polymer coagulant aqueous
solution are stored in the first coagulant aqueous solution storage
tank 31 and the second coagulant aqueous solution storage tank 1 in
the states where the median sizes (d50) in particle size
distributions are not more than 1.0 .mu.m, respectively.
[0043] When an inorganic coagulant aqueous solution is fed to the
first coagulation tank 21, rapid stirring is applied for a given
period of time with the stirrer 22 and the being processed water is
sent to the second coagulation tank 11 at the rear stage after the
inorganic coagulant aqueous solution is added and the being
processed water is stirred for a given period of time.
Successively, a polymer coagulant aqueous solution is added to the
being processed water in the second coagulation tank 11 and the
being processed water is stirred slowly for a given period of time
with the stirrer 12. The being processed water stirred slowly for a
given period of time is sent to the filtration section 9, a
coagulation formed in the being processed water is separated and
removed, and the being processed water is separated into
concentrated water and fresh water by filtration at the RO membrane
unit 10. By applying rapid stirring at the first coagulation tank
21 and applying slow stirring at the second coagulation tank 11 in
this way, it is possible to increase the particle size of flocs
that are the coagulation in the being processed water and improve
the coagulation performance. Here, an addition quantity of an
inorganic coagulant aqueous solution and an addition quantity of a
polymer coagulant aqueous solution are decided by the water quality
data obtained from the first water quality inspection section 7,
the water quality data obtained from the second water quality
inspection section 8, and a median size (d50) in the particle size
distribution of a polymer coagulant aqueous solution obtained from
the particle size distribution measurement device 50 in the same
manner as shown in FIG. 1.
[0044] A configuration of using a means for mixing a coagulant
in-line in place of a coagulation tank as shown in FIG. 1 or 2 is
explained hereunder. FIG. 3 is still another general configuration
diagram of a water processing apparatus having a coagulation
processing unit according to the present invention. A water
processing apparatus as shown in FIG. 3 is configured so as to be
provided with an in-line mixer 101 in place of the coagulation tank
11 and the stirrer 12 as shown in FIG. 1 and add a polymer
coagulant aqueous solution to being processed water at the front
stage of the in-line mixer 101 through a pump 13. Specifically, a
port allowing a polymer coagulant aqueous solution to be injected
is formed at a pipe connected to the inlet part of the in-line
mixer 101. The in-line mixer 101 has two spiral partitions facing
each other in the interior for example. Flocs that are a
coagulation are formed by applying a shear stress to the being
processed water flowing in the interior by the two spiral
partitions facing each other and mixing the polymer coagulant and
impurities contained in the being processed water. In the same
manner as shown in FIG. 1, a coagulant addition rate control
section 6 decides an addition quantity of the polymer coagulant
aqueous solution on the basis of water quality data obtained from a
first water quality inspection section 7, water quality data
obtained from a second water quality inspection section 8, and a
median size (d50) in the particle size distribution of the polymer
coagulant aqueous solution obtained from a particle size
distribution measurement device 50. When an in-line mixer 101 is
used in this way, it is necessary to set a pipe length or a pipe
diameter in order to secure reaction time after mixture, namely
time required for the polymer coagulant to trap impurities in the
being processed water.
[0045] Further, FIG. 4 is yet another general configuration diagram
of a water processing apparatus having a coagulation processing
unit according to the present invention. In a water processing
apparatus shown in FIG. 4, an in-line mixer 102 and an in-line
mixer 101 are installed in place of the first coagulation tank 21
and the stirrer 22 and the second coagulation tank 11 and the
stirrer 12 shown in FIG. 2, respectively. The structure itself of
each of the in-line mixers is the same as FIG. 3 and hence the
explanations are omitted. In the configuration shown in FIG. 4, an
inorganic coagulant aqueous solution is added to being processed
water through a pump 14 at the front stage of the in-line mixer 102
and a polymer coagulant aqueous solution is added to the being
processed water through a pump 13 at a pipe section connecting the
in-line mixer 102 to the in-line mixer 101. Here, a coagulant
addition rate control section 6 decides an addition quantity of an
inorganic coagulant aqueous solution and an addition quantity of a
polymer coagulant aqueous solution in the same manner as FIG. 2.
Further, it is necessary to set a pipe length or a pipe diameter in
order to secure reaction time after mixture in the same way as the
configuration shown in FIG. 3.
[0046] By a water processing apparatus according to the present
invention shown in FIGS. 1 to 4, it is possible to store a
coagulant aqueous solution having a median size (d50) in a particle
size distribution of not more than 1.0 .mu.m and improve the
efficiency of the coagulation processing. Further, it is possible
to materialize a maximum coagulant efficiency by the optimization
of a coagulant addition rate, prevent excessive addition of a
coagulant and unnecessary sludge from being generated, and to
optimize the operation cost of the water processing apparatus.
[0047] Here, the shapes and materials of coagulant aqueous solution
storage tanks 1 and 31 used in a water processing apparatus
according to the present invention shown in FIGS. 1 to 4 are not
particularly limited as long as they can store coagulants.
Furthermore, since the pH of a coagulant aqueous solution
influences the efficiency of coagulation processing, it is
desirable to install a pH measurement mechanism and a pH adjuster
addition mechanism.
[0048] Embodiments according to the present invention are
specifically explained together with comparative examples
hereunder.
Embodiment 1
[0049] In the present Embodiment, the configuration of a water
processing apparatus shown in FIG. 2 is used, a ferric chloride
aqueous solution of 3.8% concentration is used as an inorganic
coagulant aqueous solution stored in a coagulant aqueous solution
storage tank 31, and a polyacrylic acid-polyacrylamide copolymer
aqueous solution of 0.1% concentration is used as a polymer
coagulant aqueous solution stored in a coagulant aqueous solution
storage tank 1. Seawater is used as being processed water and a
sand filtration tank capable of removing impurities having particle
sizes of about 5 .mu.m is used as a filtration section 9. pH is set
at 5.1, the particle size distribution (d50) of the polymer
coagulant aqueous solution is set at 1.0 .mu.m, and, in order to
verify the effect of coagulation processing, being processed water
after subjected to sand filtration is taken and the total organic
carbon concentration (TOC) and the acidic sugar concentration of
the being processed water are evaluated. As a result of the
evaluation, a TOC of 0.5 ppm and an acidic sugar rejection ratio of
80% are obtained as the processed water quality.
[0050] On this occasion, as Comparative Example 1, the particle
size distribution (d50) of the polymer coagulant aqueous solution
is changed to 3.0 .mu.m and other conditions are unchanged. As a
result, a TOC of 0.6 ppm and an acidic sugar rejection ratio of 40%
are obtained as the being processed water quality.
Embodiment 2
[0051] In the present Embodiment, the configuration of a water
processing apparatus shown in FIG. 2 is used, a ferric chloride
aqueous solution of 3.8% concentration is used as an inorganic
coagulant aqueous solution stored in a coagulant aqueous solution
storage tank 31, and a polyacrylic acid-polyacrylamide copolymer
aqueous solution of 0.1% concentration is used as a polymer
coagulant aqueous solution stored in a coagulant aqueous solution
storage tank 1. Seawater is used as being processed water and a
sand filtration tank capable of removing impurities having particle
sizes of about 5 .mu.m is used as a filtration section 9. pH is set
at 5.1, the particle size distribution (d50) of the polymer
coagulant aqueous solution is set at 0.7 .mu.m, and, in order to
verify the effect of coagulation processing, being processed water
after subjected to sand filtration is taken and the total organic
carbon concentration (TOC) and the acidic sugar concentration of
the being processed water are evaluated. As a result of the
evaluation, a TOC of 0.5 ppm and an acidic sugar rejection ratio of
82% are obtained as the being processed water quality.
[0052] On this occasion, as Comparative Example 2, the particle
size distribution (d50) of the polymer coagulant aqueous solution
is changed to 1.5 .mu.m and other conditions are unchanged. As a
result, a TOC of 0.6 ppm and an acidic sugar rejection ratio of 55%
are obtained as the being processed water quality.
Embodiment 3
[0053] In the present Embodiment, the configuration of a water
processing apparatus shown in FIG. 2 is used, a ferric chloride
aqueous solution of 3.8% concentration is used as an inorganic
coagulant aqueous solution stored in a coagulant aqueous solution
storage tank 31, and a polyacrylic acid-polyacrylamide copolymer
aqueous solution of 0.1% concentration is used as a polymer
coagulant aqueous solution stored in a coagulant aqueous solution
storage tank 1. Seawater is used as being processed water and a
sand filtration tank capable of removing impurities having particle
sizes of about 5 .mu.m is used as a filtration section 9. pH is set
at 5.1, the particle size distribution (d50) of the polymer
coagulant aqueous solution is set at 0.3 .mu.m, and, in order to
verify the effect of coagulation processing, being processed water
after subjected to sand filtration is taken and the total organic
carbon concentration (TOC) and the acidic sugar concentration of
the being processed water are evaluated. As a result of the
evaluation, a TOC of 0.4 ppm and an acidic sugar rejection ratio of
85% are obtained as the being processed water quality.
[0054] On this occasion, as Comparative Example 3, the particle
size distribution (d50) of the polymer coagulant aqueous solution
is changed to 1.1 .mu.m and other conditions are unchanged. As a
result, a TOC of 0.5 ppm and an acidic sugar rejection ratio of 72%
are obtained as the processed water quality.
Embodiment 4
[0055] In the present Embodiment, the configuration of a water
processing apparatus shown in FIG. 2 is used, a ferric chloride
aqueous solution of 3.8% concentration is used as an inorganic
coagulant aqueous solution stored in a coagulant aqueous solution
storage tank 31, and a polyacrylic acid aqueous solution of 0.1%
concentration is used as a polymer coagulant aqueous solution
stored in a coagulant aqueous solution storage tank 1. Seawater is
used as being processed water and a sand filtration tank capable of
removing impurities having particle sizes of about 5 .mu.m is used
as a filtration section 9. pH is set at 3.7, the particle size
distribution (d50) of the polymer coagulant aqueous solution is set
at 1.0 .mu.m, and, in order to verify the effect of coagulation
processing, being processed water after subjected to sand
filtration is taken and the total organic carbon concentration
(TOC) and the acidic sugar concentration of the being processed
water are evaluated. As a result of the evaluation, a TOC of 0.5
ppm and an acidic sugar rejection ratio of 82% are obtained as the
being processed water quality.
[0056] On this occasion, as Comparative Example 4, the particle
size distribution (d50) of the polymer coagulant aqueous solution
is changed to 3.0 .mu.m and other conditions are unchanged. As a
result, a TOC of 0.6 ppm and an acidic sugar rejection ratio of 42%
are obtained as the being processed water quality.
Embodiment 5
[0057] In the present Embodiment, the configuration of a water
processing apparatus shown in FIG. 2 is used, a ferric chloride
aqueous solution of 3.8% concentration is used as an inorganic
coagulant aqueous solution stored in a coagulant aqueous solution
storage tank 31, and a polyacrylic acid aqueous solution of 0.1%
concentration is used as a polymer coagulant aqueous solution
stored in a coagulant aqueous solution storage tank 1. Seawater is
used as being processed water and a sand filtration tank capable of
removing impurities having particle sizes of about 5 .mu.m is used
as a filtration section 9. pH is set at 3.7, the particle size
distribution (d50) of the polymer coagulant aqueous solution is set
at 0.7 .mu.m, and, in order to verify the effect of coagulation
processing, being processed water after subjected to sand
filtration is taken and the total organic carbon concentration
(TOC) and the acidic sugar concentration of the being processed
water are evaluated. As a result of the evaluation, a TOC of 0.4
ppm and an acidic sugar rejection ratio of 86% are obtained as the
being processed water quality.
[0058] On this occasion, as Comparative Example 5, the particle
size distribution (d50) of the polymer coagulant aqueous solution
is changed to 1.5 .mu.m and other conditions are unchanged. As a
result, a TOC of 0.6 ppm and an acidic sugar rejection ratio of 59%
are obtained as the being processed water quality.
Embodiment 6
[0059] In the present Embodiment, the configuration of a water
processing apparatus shown in FIG. 2 is used, a ferric chloride
aqueous solution of 3.8% concentration is used as an inorganic
coagulant aqueous solution stored in a coagulant aqueous solution
storage tank 31, and a polyacrylic acid aqueous solution of 0.1%
concentration is used as a polymer coagulant aqueous solution
stored in a coagulant aqueous solution storage tank 1. Seawater is
used as being processed water and a sand filtration tank capable of
removing impurities having particle sizes of about 5 .mu.m is used
as a filtration section 9. pH is set at 3.7, the particle size
distribution (d50) of the polymer coagulant aqueous solution is set
at 0.3 .mu.m, and, in order to verify the effect of coagulation
processing, being processed water after subjected to sand
filtration is taken and the total organic carbon concentration
(TOC) and the acidic sugar concentration of the processed water are
evaluated. As a result of the evaluation, a TOC of 0.4 ppm and an
acidic sugar rejection ratio of 90% are obtained as the being
processed water quality.
[0060] On this occasion, as Comparative Example 6, the particle
size distribution (d50) of the polymer coagulant aqueous solution
is changed to 1.1 .mu.m and other conditions are unchanged. As a
result, a TOC of 0.5 ppm and an acidic sugar rejection ratio of 75%
are obtained as the processed water quality.
Embodiment 7
[0061] In the present Embodiment, the configuration of a water
processing apparatus shown in FIG. 2 is used, a ferric chloride
aqueous solution of 3.8% concentration is used as an inorganic
coagulant aqueous solution stored in a coagulant aqueous solution
storage tank 31, and a polyacrylic acid-polyacrylamide copolymer
aqueous solution of 0.1% concentration is used as a polymer
coagulant aqueous solution stored in a coagulant aqueous solution
storage tank 1. Seawater is used as being processed water and a
sand filtration tank capable of removing impurities having particle
sizes of about 5 .mu.m is used as a filtration section 9. pH is set
at 1.0, the particle size distribution (d50) of the polymer
coagulant aqueous solution is set at 1.0 .mu.m, and, in order to
verify the effect of coagulation processing, being processed water
after subjected to sand filtration is taken and the total organic
carbon concentration (TOC) and the acidic sugar concentration of
the being processed water are evaluated. As a result of the
evaluation, a TOC of 0.5 ppm and an acidic sugar rejection ratio of
83% are obtained as the being processed water quality.
[0062] On this occasion, as Comparative Example 7, pH is changed to
8.0 and other conditions are unchanged. As a result, a TOC of 0.6
ppm and an acidic sugar rejection ratio of 45% are obtained as the
being processed water quality.
Embodiment 8
[0063] In the present Example, the configuration of a water
processing apparatus shown in FIG. 2 is used, a ferric chloride
aqueous solution of 3.8% concentration is used as an inorganic
coagulant aqueous solution stored in a coagulant aqueous solution
storage tank 31, and a polyacrylic acid aqueous solution of 0.1%
concentration is used as a polymer coagulant aqueous solution
stored in a coagulant aqueous solution storage tank 1. Seawater is
used as being processed water and a sand filtration tank capable of
removing impurities having particle sizes of about 5 .mu.m is used
as a filtration section 9. pH is set at 1.0, the particle size
distribution (d50) of the polymer coagulant aqueous solution is set
at 1.0 .mu.m, and, in order to verify the effect of coagulation
processing, being processed water after subjected to sand
filtration is taken and the total organic carbon concentration
(TOC) and the acidic sugar concentration of the being processed
water are evaluated. As a result of the evaluation, a TOC of 0.4
ppm and an acidic sugar rejection ratio of 86% are obtained as the
being processed water quality.
[0064] On this occasion, as Comparative Example 8, pH is changed to
8.0 and other conditions are unchanged. As a result, a TOC of 0.6
ppm and an acidic sugar rejection ratio of 51% are obtained as the
being processed water quality.
[0065] Embodiments 1 to 8 and Comparative Examples 1 to 8 stated
above are summarized. FIG. 6 is a table explaining the relationship
between a particle size distribution and a being processed water
quality at each of the Examples and FIG. 7 is a table explaining
the relationship between a particle size distribution and a being
processed water quality at each of the comparative Examples.
[0066] In FIGS. 6 and 7, Embodiment 1 and Comparative Example 3,
those being the cases of using a polyacrylic acid-polyacrylamide
copolymer aqueous solution of 0.1% concentration as a polymer
coagulant aqueous solution and setting pH at 5.1, are examined.
Whereas the particle size distribution (d50) is 1.0 .mu.m and the
being processed water quality is a TOC of 0.5 ppm and an acidic
sugar rejection ratio of 80% in Embodiment 1, the particle size
distribution (d50) is 1.1 .mu.m and the being processed water
quality is a TOC of 0.5 ppm and an acidic sugar rejection ratio of
72% in Comparative Example 3. That is, TOC shows an identical value
but only the acidic sugar rejection ratio shows different values of
80% and 72%.
[0067] Likewise, Embodiment 4 and Comparative Example 6, those
being the cases of using a polyacrylic acid aqueous solution of
0.1% concentration as a polymer coagulant aqueous solution and
setting pH at 3.7, are examined. Whereas the particle size
distribution (d50) is 1.0 .mu.m and the being processed water
quality is a TOC 0.5 ppm and an acidic sugar rejection ratio of 82%
in Embodiment 4, the particle size distribution (d50) is 1.1 .mu.m
and the being processed water quality is a TOC of 0.5 ppm and an
acidic sugar rejection ratio of 75% in Comparative Example 6. TOC
shows an identical value but only the acidic sugar rejection ratio
shows different values of 82% and 75%.
[0068] Attention is paid here to an acidic sugar rejection ratio
and it is found that, when a water processing apparatus shown in
FIG. 2 that is one of the embodiments according to the present
invention is operated, the load in a second coagulation tank 11 and
an RO membrane unit 10 installed at the rear stage of a filtration
section 9 varies largely between above and below an acidic sugar
rejection ratio of 80%. That is, the change rate of clogging
(filtration pressure rise) speed of a membrane is correlated with
an acidic sugar rejection ratio and varies largely between above
and below an acidic sugar rejection ratio of 80%. FIG. 8 is a graph
showing the relationship between an acidic sugar rejection ratio
and an ascension rate of clogging (filtration pressure). The
results obtained by feeding several kinds of being processed water
having different acidic sugar rejection ratios to an RO membrane
unit 10 and obtaining and plotting the ascension rates of clogging
(filtration pressure) on those occasions are shown in FIG. 8. As
shown in FIG. 8, when an acidic sugar rejection ratio is less than
80%, the ascension rate of clogging shows a large value and the
change rate A is small. In contrast, when an acidic sugar rejection
ratio is not less than 80%, the ascension rate of clogging lowers
rapidly and the change rate B is larger than the change rate A.
That is, by controlling an acidic sugar rejection ratio to not less
than 80%, the clogging prevention effect at an RO membrane unit 10
improves conspicuously. Consequently, it is obvious that it is
possible to obtain a high clogging prevention effect by setting a
median size (d50) in the particle size distribution of a coagulant
aqueous solution at not more than 1.0 .mu.m.
[0069] Further, the lower limit of a median size (d50) in the
particle size distribution of a coagulant aqueous solution is set
on the assumption that a polymer coagulant dissolves completely.
That is, atoms constituting a polymer coagulant are three elements
of C, H, and O and a lower limit median size of 1.4 nm is obtained
by computing the length of a polymer and an area occupied by the
polymer from the covalent radii of them. Consequently, it is
desirable to set a median size in the particle size distribution of
a polymer coagulant aqueous solution used in the present invention
at not less than 1.4 nm to not more than 1.0 .mu.m.
[0070] Furthermore, in comparison between Embodiment 1 and
Embodiment 7, the median sizes (d50) in the particle size
distributions of the polymer coagulant aqueous solutions are an
identical value of 1.0 .mu.m but only pH is different and is 5.1 in
Embodiment 1 and 1.0 in Embodiment 7. Whereas the being processed
water quality is a TOC of 0.5 ppm and an acidic sugar rejection
ratio of 80% in Embodiment 1, the being processed water quality is
a TOC of 0.5 ppm and an acidic sugar rejection ratio of 83% in
Embodiment 7.
[0071] Moreover, in comparison between Embodiment 4 and Embodiment
8, the median sizes (d50) in the particle size distributions of the
polymer coagulant aqueous solutions are an identical value of 1.0
.mu.m but only pH is different and is 3.7 in Embodiment 4 and 1.0
in Embodiment 8. Whereas the being processed water quality is a TOC
of 0.5 ppm and an acidic sugar rejection ratio of 82% in Embodiment
4, the being processed water quality is a TOC of 0.4 ppm and an
acidic sugar rejection ratio of 86% in Embodiment 8.
[0072] In this way, it is possible to obtain a clogging prevention
effect in an RO membrane unit 10 installed at a rear stage as
stated above by controlling a median size (d50) in the particle
size distribution of a polymer coagulant aqueous solution used in
the present invention to not more than 1.0 .mu.m, and further
improve an acidic sugar rejection ratio and the clogging prevention
effect by lowering the pH of the polymer coagulant aqueous solution
(in an acidic state). Here, it is preferable to adjust pH so as to
be not more than 1.0 by adding a pH adjuster.
[0073] Here, the present invention is not limited to the
configurations of the embodiments described above and includes
various modified examples. For example, the embodiments are the
examples explained in detail in order to explain the present
invention in an understandable way, and are not always limited to
embodiments including all the configurations explained above.
Further, it is also possible to replace a part of a configuration
in an embodiment with the configuration of another embodiment, or
add the configuration of another embodiment to the configuration of
an embodiment. Furthermore, it is also possible to add, delete, and
replace the configuration of another embodiment with regard to a
part of the configuration of each of the embodiments.
EXPLANATIONS OF REFERENCE NUMERALS
[0074] 1 Coagulant aqueous solution storage tank [0075] 2 Flow cell
[0076] 3 Laser irradiation section [0077] 4 Detection section
[0078] 5 Stirrer [0079] 6 Coagulant addition rate control section
[0080] 7 First water quality inspection section [0081] 8 Second
water quality inspection section [0082] 9 Filtration section [0083]
10 RO membrane unit [0084] 11 Coagulation tank [0085] 20 Branched
channel for particle size distribution measurement [0086] 50
Particle size distribution measurement device [0087] 101 In-line
mixer
* * * * *